A pottery wheel, also known as a potter's wheel or potter's lathe, is a machine used to facilitate forming, trimming, decorating and other manipulation techniques of pottery. At a basic level, a potter's wheel is a device that provides rotation to a workpiece or “form”, such as an unformed piece of clay or a preformed shape. As the art of pottery has existed for centuries, pottery wheels have taken many different forms. A typical modern-day pottery wheel includes a frame, a power source (such as a motor or kickwheel) and a wheelhead coupled to the power source such that the power source rotates the wheelhead. Some pottery wheels include attached work tables and splash pans that surround the wheelhead to catch any trimmings or other debris thrown off the wheelhead by centrifugal force as the wheelhead rotates.
The wheelhead provides a rotating planar upper-surface on which a potter can work a workpiece or form. Wheelheads can take any form and size, but a typical wheelhead is a planar disc of metal or other sturdy material, such as cast aluminum, and includes concentric markings or rings on the top surface about the center of the wheelhead. The concentric markings or rings aid a potter in centering a workpiece, especially a workpiece with a circular or other symmetrical profile.
Wheelheads often also include mechanisms for selectively attaching a bat (also known as a batt or batten) to the upper surface of the wheelhead. A batt can allow for removal of a workpiece from the wheel without damaging or deforming the workpiece. A batt can also simply provide an alternative working surface to suit a potter's tastes. For example, some potters prefer to shape or “throw” clay on plaster, therefore bucket-style wheelheads have been designed to allow for plaster bats. However, wheelheads more commonly include bat pins and/or bat pin apertures that mate with corresponding bat pins or bat pin apertures in the bat to secure the bat to the wheelhead. Such mechanisms aid in adding centripetal force to a bat to secure the bat to the wheelhead such that the bat rotates with the wheelhead and is prevented from disengaging from the wheelhead due to centrifugal force.
Similar to bats, other devices are occasionally applied to the upper surface of a wheelhead via the bat pins and bat bin apertures to facilitate certain pottery processes. In particular, prior art devices for centering and temporarily holding pottery forms, such as semi-pliable greenware bowls, cups and vases, on the wheelhead are known in the art. Such devices aim to reduce or eliminate off-center rotation, wobble and the like to facilitate shaping, forming and finishing of workpieces. More specifically, some devices facilitate the removal of excess clay from the bottom area of the workpiece to create a foot. A foot is typically a circular ring on the bottom of the workpiece formed by the removal of material with a trimming tool as the workpiece rotates on the wheel. The foot provides a level (if desired) stable base for the workpiece. With circular workpieces, or other symmetrical forms, the foot is usually formed about the center of the workpiece so that the workpiece is symmetric and thus aesthetically pleasing.
One popular prior art wheelhead device for centering and temporarily holding pottery forms to facilitate shaping and formation of a foot is the Giffin device, disclosed in U.S. Pat. No. 4,222,577. The Giffin '577 device essentially is a three jaw self-centering chuck, like the typical chuck of a power tool. The Giffin '577 device uses three sliding arms (like the jaws of a common chuck) interconnected via a spiral groove in a bottom plate (i.e., a scroll plate) to center and hold a workpiece. As the spiral groove is concentric about the center of the bottom plate and the movement of the sliding arms is fixed with respect to one another (i.e., the sliding arms move in unison), the sliding arms self-center a circular workpiece placed therebetween as they slide within the spiral groove and move towards the center of the plate. In this way, the sliding arms of the Giffin '577 device securely hold and self-center a circular workpiece.
One of the drawbacks encountered with prior art wheelhead devices for centering and securely holding workpieces is that they can only provide three points of contact with the outer surface of a workpiece, such as with the Giffin device described above. While three points of contact may be sufficient to secure circular or three-sided workpieces, three points of contact are not sufficient for some uniquely shaped workpieces. For example, square, rectangular, other multi-sided forms with 4 or more sides, oblong, bisymmetric, asymmetric, abstract curvilinear and other non-circular, irregular or “organic” shapes often cannot be fully supported with three points of contact. When these types of irregular or organic workpieces are not fully supported, they may slide, twist or otherwise move on the device during rotation thereof. Movement of workpieces during rotation prevents a potter from being able to create a circular foot, can break or distort the workpiece, or, in the worst case scenario, can eject the workpiece from the pottery wheel.
Another drawback encountered with prior art wheelhead devices for centering and securely holding workpieces is that the support members of the devices are spatially locked with respect to one another and the center of the device (thus the support members move in unison) and are positioned symmetrically about the center of the device. Therefore, in the prior art devices with three support members, the support members are equally spaced with respect to the center of the device and each support member is spaced about 120 degrees from an adjacent support member. In such a fixed symmetric relationship, the support members are unable to fully support an irregular or organic workpiece—as it is likely that only two support members will contact a workpiece.
Similarly, even symmetric non-circular workpieces will not be fully supported by the fixed symmetrically disposed support members of these prior art devices. In use of such devices with support members in a “locked” arrangement, a single support member will likely first contact the exterior surface of the workpiece. If the support members are further extended toward the center of the device, the lone support member contacting the workpiece will push or twist the workpiece until at least one other support member contacts the outer surface of the workpiece. At this stage, the workpiece is not fully supported. If the support members are extended even further, the support members will either deform the workpiece or the workpiece will further slide and/or until another support member contacts the outer surface of the workpiece. At this point, if the device only has three support members (as in the prior art), the workpiece has been translated about the device into an arrangement where the outer surfaces of the workpiece that are in contact with the support members are radially equidistant from one another and from the center of the device. However, because the workpiece is non-circular, the true center of the workpiece is not aligned with the center of the device. In such a non-centered arrangement, a foot cannot be formed in the center of the workpiece, and the potter has no ability to select the position of the foot. Further, as is understood in the art, such pushing and twisting of the workpiece about the device will scratch, deform or otherwise mar the workpiece. Still further, in all likelihood, an irregular or non-circular symmetric workpiece will not define three outer surface locations that are radially equidistant from one another and from a central point, and therefore a third support member would never reach the outer surface of such a workpiece (at least without deforming the workpiece).
Yet another drawback encountered with prior art wheelhead devices for centering and securely holding workpieces is that the workpieces, including circular workpieces, cannot be selectively secured in locations other than the center of the device. For certain processes, a potter may wish to secure a workpiece off-center from the axis of rotation. For example, in order to apply glaze in an uneven and aesthetically pleasing pattern, potters would prefer to place a workpiece off-center and apply a glaze soaked applicator against the outer surface of the workpiece. By keeping the applicator in the same position with respect to the axis of rotation, the off-center rotation or “wobbling” of the workpiece would create thinner, wider and/or random patterns of glaze on the workpiece's outer surface. Further, the location of the foot of workpieces cannot be chosen by the potter. As described above, prior art devices are self-centering because the support members are in a fixed relationship and symmetrically opposed about the center of the device. Thus, these prior art devices automatically center and support a workpiece (i.e., when the last support member contacts the outer surface of a circular workpiece, the workpiece is centered and fully supported). Thereby, such an arrangement and configuration of the support members in the prior art devices prevents a potter from securing workpieces anywhere else besides the center of the device (including circular workpieces), i.e., the self-centering feature prevents the potter from deciding where to secure a workpiece. As a result, the prior art devices do not allow a potter to select the secured position and orientation of a workpiece, and therefore do not allow the potter to elect where the foot of a particular workpiece should be formed, such as circular workpieces, or apply such an “uneven” glaze process.
Still further, the fixed symmetrical arrangement of the support members of prior art devices does not allow the potter to control where irregular shaped workpieces are secured on the devices (assuming an irregular shaped workpiece can actually be secured). Even if a prior art wheelhead device can secure a particular irregular or asymmetric workpiece without destroying the workpiece, the workpiece would be automatically positioned (as discussed above), and the potter thus had no ability to select the secured position. As a result, the prior art devices do not allow a potter to select the secured position and orientation of an irregular or non-circular symmetric workpiece, and therefore do not allow the potter to elect where the foot of a particular irregular or non-circular symmetric workpiece should be formed.
Another drawback encountered with prior art wheelhead devices for centering and securely holding workpieces is that the devices are thick and thereby significantly elevate workpieces with respect to the wheelhead. A thick wheelhead device, and therefore an elevated workpiece, will allow trimmings or other debris thrown off the wheelhead by centrifugal force to be thrown at a higher trajectory as compared to if the device was not used. Splash pans are typically designed or configured based on the height of the wheelhead of a potter wheel. Therefore, if a particular pottery wheel includes a splash pan, workpieces that are significantly elevated with respect to the wheelhead will tend to throw trimmings or other debris past or over the splash pan. As such, prior art wheelhead devices for centering and securely holding workpieces that are thick tend to elevate workpieces to such an extent that they eliminate or reduce the debris capture advantages of splash pans.
Yet another drawback encountered with prior art wheelhead devices for centering and securely holding workpieces is that they only function properly with a particular direction of rotation. Prior art devices are designed for either clockwise or counter-clockwise rotation of the pottery wheel. Prior art devices, like the Giffin device described above, include support members held in slots of a top plate and in a spiral groove of a bottom scroll plate. The spiral groove provides for translation of the support members within the slot along a radius of the device as the scroll plate and top plate rotate with respect to one another (i.e., as the support members move angularly along the spiral, they move closer or farther away from the center of the device). However, the spiral groove is limited to providing movement towards the center of the device only when the support members rotate about the spiral groove either in a clockwise or counter-clockwise direction, depending upon if the spiral groove spirals from the outer edge to the center in a clockwise or counter-clockwise direction. As a result, if a clockwise designed prior art device were installed on a pottery wheelhead that rotated counter-clockwise, the support members would be biased away from the workpiece during rotation of the wheelhead, and thus fail to support the workpiece. The same lack of support would occur if a counter-clockwise designed prior art device were installed on a pottery wheelhead that rotated clockwise.
Accordingly, it is an object of the present invention to overcome one or more of the above-described drawbacks and/or disadvantages of the prior art.